1. Field of the Invention
The present invention relates to an optical fiber for wavelength-division-multiplexing (WDM) transmission and an optical communication system that employs the optical fiber.
2. Description of the Related Art
Recently, research and development for WDM transmission technologies are actively performed, and further expansion of a transmission band is required. In response to the request, development of non-zero dispersion shifted optical fiber (NZ-DSF) with a reduced dispersion slope is highly focused, aiming at expansion of the transmission band. A reduced dispersion slope NZ-DSF keeps an absolute value of dispersion appropriately and suppresses an absolute value of dispersion slope.
A reduced dispersion slope NZ-DSF is proposed in U.S. Pat. No. 6,856,744, in which an absolute value of dispersion at a wavelength of 1550 nm is equal to or more than 4 ps/nm/km and equal to or less than 10 ps/nm/km, an absolute value of dispersion slope is equal to or less than 0.04 ps/nm2/km, and an effective area is 40 μm2.
However, a refractive index profile of the reduced dispersion slope NZ-DSF disclosed in the above literature is based on an optical fiber with a core including four or five layers, which is more complex than a conventional NZ-DSF. Although desired dispersion, dispersion slope, and Aeff may be obtained more easily by designing the core in four or five layers, it is difficult to reduce a transmission loss, and a production cost becomes high.